1. Field of the Invention
The invention relates to a remaining amount of developer detection device, a development device, a process unit, and an image forming apparatus, and more specifically, to a remaining amount of developer detection device capable of detecting an amount of toner remaining in a development device included in an image forming apparatus such as copier, a printer, and a facsimile machine.
2. Description of the Related Art
The related art image forming apparatus having an electrophotographic system generally includes a development device configured to form an electrostatic latent image on the surface of an image carrier and provide a developer on the electrostatic latent image to develop the electrostatic latent image, thereby forming a visible image. The developer system of the image forming apparatus includes two major systems: 1) a two-component developer system; and 2) a single-component developer system. The two-component developer system employs a developer containing toner and a magnetic carrier, and the single-component developer system employs a developer containing toner only without a magnetic carrier. The single-component developer system further includes subsystems, namely, a magnetic single-component toner system and non-magnetic single-component toner system.
In the single-component system, since this type of developer does not contain a magnetic carrier, it is not necessary to mix the toner and the magnetic carrier by stirring. Thus, the development device for the single-component system can be made simpler and smaller in size than the development device for the two-component developer system.
However, toner is consumable and is contained in a cartridge, which is placed in a cartridge holder of the development device. The amount of toner decreases as the number of printed images increases. Since the cartridge of the toner attached to the cartridge holder (hereinafter called a “toner container chamber”) is located inside a developer unit of the development device, it is hard to check the remaining amount of toner from outside of the development device with the naked eye. Thus, the toner container chamber generally includes a sensor unit for detecting the remaining amount of toner. That is, the development device includes a remaining amount of toner detection sensor that detects the amount of toner, such as a piezoelectric element, and generates, upon detection of shortage of toner, a signal to notify a user of the shortage by displaying an alarm. Thus, the user is notified by the display of the shortage of toner, so that the user can replace the development device with a new one, or replace the toner cartridge with a new one. As described above, in order to detect the remaining amount of toner, it is preferable to provide a remaining amount of toner detection sensor in the development device or a process unit containing the development device. However, these days image forming apparatuses are desired to be reduced in size and prices, and therefore development devices utilized for such apparatuses are also desired to contain low-price sensors.
As the related art technology for detecting a remaining amount of toner, Japanese Utility Model Registration Application Laid-Open Publication No. 62-118248 discloses a toner near-end detecting device for detecting the shortage of toner. The disclosed toner near-end detecting device includes a scooper scooping the toner remaining in a toner hopper and a toner detector with which the toner remaining in the toner hopper is brought into contact to generate a signal based on the contact load of the toner.
Japanese Patent Application Laid-Open Publication No. 02-20887 also discloses a similar technology, that is, a remaining amount of toner detection device for detecting the remaining amount of toner. The disclosed remaining amount of toner detection device includes a lever moving upward and downward in a toner container chamber and pressing toner when moving downward in the toner container chamber, and a lever movement detector detecting one end of the lever projecting from the toner container chamber. However, those toner detecting devices disclosed in the two publications above are configured to detect the amount of toner remaining in the toner hopper. This indicates that the disclosed toner detecting devices do not detect the amount of toner remaining near a development roller. The toner remaining near the development roller is directly used for developing images. Accordingly, the disclosed toner detecting devices may have low accuracy in detecting the remaining amount of the toner used for developing images. Further, it is difficult to reduce sizes of these devices. Moreover, these devices include a movable member for detecting the remaining amount of toner, and as a result, the devices have a complex structure.
Meanwhile, when a rotary member of the device such as a stirring member is rotated to stir the toner, the toner may be caught in an interspace between a rotary shaft and a shaft bearing. The toner stuck between the shaft and bearing melts due to friction heat generated from the rotary shaft, which inhibits the shaft from rotating. Japanese Patent Application Laid-Open Publication No. 11-194598 discloses a powder container chamber provided for a development device. The powder container chamber contains powder, and includes a rotor having a shaft rotated based on a shaft end slotted into a bearing hole in an internal wall of the container chamber, the shaft end having a screw groove cut in a direction returning to the inside of the container chamber from a rotating direction of the rotor. Japanese Patent Application Laid-Open Publication No. 2006-098916 discloses a development device that includes a developer exclusion member attached to a rotating shaft of a development roller supported by a bearing member in a housing, and a bearing supporting the rotating shaft. In the development device, lubricant is supplied in an interspace between the developer exclusion member and the bearing. However, the technology disclosed by Japanese Patent Application Laid-Open Publication No. 11-194598 may not sufficiently remove the toner that is stuck in an interspace between the bearing and the shaft. Further, the technology disclosed by Japanese Patent Application Laid-Open Publication No. 11-194598 may not sufficiently prevent the toner from being stuck in the interspace between the shaft and shaft bearing member. In this technology, the lubricant catches toner stuck in the interspace between the shaft and shaft bearing member to prevent the toner from sticking. Thus, if a large amount of the toner is supplied, the disclosed technology may not sufficiently prevent the toner from sticking in the interspace.
As another method of excluding the toner, there is disclosed a toner remaining amount detector that is provided in the toner container chamber. The disclosed toner remaining amount detector mechanically detects a remaining amount of toner. For example, Japanese Patent Application Laid-Open Publication No. 10-319704 discloses a development device 8a (reference numerals provided herein are employed from the disclosed references) having a developer container chamber 8, a stirring bar 11 moving straightforward according to resistance against the toner 5 increased by stirring the toner 5, and a sensor 12 detecting a moving state of the stirring bar 11, thereby detecting the remaining amount of toner. The stirring bar 11 includes an arm base 11b and an arm point 11a shaft connected to the arm base lib, so that the stirring bar 11 can be bent in a rotational direction of the stirring bar 11. In the development device 8, the sensor 12 is located such that the sensor 12 generates an alarm when the amount of toner reaches a desired position. In this development device 8, when the toner amounts to a certain amount where an alarm is generated, the stirring bar 11 is bent in a rotational direction of the stirring bar 11 so that the sensor 12 does not detect the end point of the stirring bar 11. Accordingly, it is possible to realize stepwise detection of the remaining amount of toner in the developer container chamber 8a. Further, Japanese Patent Application Laid-Open Publication No. 11-84850 discloses a development device in which a toner contained in a toner container chamber 10a is transferred toward a development roller 10d by toner transfer member 10b that rotatably transfers the developer. In this development device, a gear coupled with a driver source is provided with an end of the toner transfer member 10b, an encoder plate 16 projecting outside of the toner container chamber 10a is provided with the other end of the toner transfer member 10b, and a photosensor 17 having a luminous unit 17a and a photodetecting unit 17b is provided to cover the periphery of the encoder plate 16. The photosensor generates a pulse wave according to rotation of the encoder plate 16, and monitors the pulse wave, so that a toner near end of the toner container chamber 10a and a toner near end of the development device can both be detected. Moreover, Japanese Patent Application Laid-Open Publication No. 11-174812 discloses a development device in which a float 1 is provided in a toner container chamber A, and the remaining amount of the toner is detected by causing an angle sensor to read the position of the float 1, thereby notifying a user of the remaining amount of the toner.
However, with this method, the remaining amount of toner detection unit detects only an approximate amount of the toner remaining in the container chamber, indicating to a user that soon no toner will be left in the container chamber, and does not notify the user of an accurate amount of the toner remaining in the container chamber at each detection.
Further, there is disclosed a technology in which the amount of toner consumed can be sequentially detected in an image forming apparatus. A method in which the amount of toner consumption is sequentially detected is disclosed in Japanese Patent Application Laid-Open Publication No. 2007-298721. With this technology, the number of pixels is counted based on image data, and the amount of the toner consumption can be determined based on the counted pixels of the image data. The counted pixels may also be corrected based on density of the image, so that a more accurate remaining amount of toner can be computed.
However, with the above sequential detection model, the number of pixels is counted based on the image data, and the amount of the toner consumption can be determined based on the counted pixels of the image data. With this model, errors in computing the consumed amount of toner may be generated according to types of the images such as an image formed of lines and an image formed of separate dots.
Further, various technologies or methods disclosed above may be combined so as to detect the remaining toner stepwise, or to detect the remaining toner more accurately. For example, Japanese Patent Application Laid-Open Publication No. 9-120248 discloses a development device including a remaining amount of toner detection unit 9 detecting toner 7 stored in a developer container chamber 6 and a storage unit 6. In this development device, the remaining amount of toner detection unit 9 detects the remaining amount of toner in the developer container chamber 6 by detecting electrostatic capacity between an electrode and a developing sleeve 3, and the storage unit 60 stores a counted value based on an image signal. When the remaining amount of toner detection unit 9 detects the remaining amount of toner amounting equal to or less than a predetermined value, the remaining amount of toner detection unit 9 initiates counting the value to compute the remaining amount of toner based on the counted value, thereby detecting a toner-near-end, indicating an amount of the toner being approximately zero. Japanese Patent Application Laid-Open Publication No. 2001-183898 discloses an image forming apparatus that includes an optical transmission sensor 5 and a pixel value counting unit 2. In this image forming apparatus, when printing starts, both the optical transmission sensor 5 and the pixel value counting unit 2 detect the remaining amount of toner. If the optical transmission sensor 5 detects the amount of toner being equal to or less than a predetermined amount, an accumulated count value counted by the pixel value counting unit 2 is corrected based on the detected amount of toner, and the remaining amount of toner is displayed based on the corrected count value.
Japanese Patent Application Laid-Open Publication No. 2006-267528 discloses an image forming apparatus that includes an image forming unit 5 having a toner container chamber unit 24 and a toner sensor lever 25 located at a distance from a supplying roller 29, the toner sensor lever 25 being rotatable and having a crank shape. The image forming apparatus further includes a sensor 25a that detects a crank shift of the toner sensor lever 25 so that the amount of toner remaining in the toner container chamber unit 24 is equal to or less than a predetermined value. Further, when the sensor 25a detects the amount of toner being equal to or less than the predetermined value, a video processing circuit initiates dot counting, and reports that a toner-near-end condition indicating the toner is approximately zero if the amount of toner reaches a predetermined value.
However, with the combination of various detecting units or methods, computing the remaining amount of toner inevitably generates errors according to positions of the sensors or timing at which sensor detection is switched to pixel count detection. Moreover, in this apparatus, a mechanical toner remaining amount detection unit provided in a toner container chamber interferes with a flow of toner around a development roller, and the mechanical toner remaining amount detection unit may not detect the remaining amount of toner accurately if toner container chamber surfaces have local curves.